--- a/model/prov-constraints.html	Mon Jul 23 13:58:53 2012 +0100
+++ b/model/prov-constraints.html	Mon Jul 23 14:12:02 2012 +0100
@@ -2905,7 +2905,20 @@
 <h2>Type Constraints</h2>
 
 <p id="typing_text">The following rule  establishes types denoted by identifiers from their use within expressions. 
-The following types are recognized: 'entity', 'activity', 'agent', 'prov:Collection', 'prov:EmptyCollection'. An identifier may denote multiple types, hence <span class="name">typeOf(id)</span> is the set of types denoted by <span class="name">id</span>. </p>
+For this, the function <span class="name">typeOf</span> gives the set of types denoted by an identifier.
+For instance,  <span class="name">typeOf(e)</span> returns the set of types associated with identifier  <span class="name">e</span>. The function <span class="name">typeOf</span> is not a term of PROV, but a construct introduced to validate PROV statements. 
+</p>
+
+<p>
+The following types are recognized: 'entity', 'activity', 'agent', 'prov:Collection', 'prov:EmptyCollection'. For identifiers that do not have a type,  <span class="name">typeOf</span> gives the empty set.
+</p>
+
+<p>To check if a PROV instance satisfies type constraints, one obtains the types of identifiers by application of
+<a class="rule-ref" href="#typing"><span>TBD</span></a>
+and check no impossibility results from rules
+<a class="rule-ref" href="#entity-activity-disjoint"><span>TBD</span></a> and
+<a class="rule-ref" href="#membership-empty-collection"><span>TBD</span></a>.</p>
+
 
 <div class='constraint' id="typing">